The study consists of two parts: The first part examines the effect of mCPP, a drug that activates obsessive-compulsive symptoms combined with psychological provocation on cerebral blood flow. The second part examines the effect of metergoline, a drug that blocks the serotonergic effects of fluvoxamine on cerebral blood flow of medicated obsessive- compulsive symptoms. The first part of the study was completed. Subjects received two SPECT scans each, one after placebo and exposure to a neutral recording and a second scan after mCPP and listening to a symptom provoking recording. We have analyzed the scans and found changes in cerebral blood flow involving the prefrontal cortex, as well as limbic and paralimbic systems. The second part of the study is still in progress. Two more patients need to be scanned to complete the study. Changes in the scans suggest that blocking the effect of a medication is effective in obsessive- compulsive disorder produced cerebral blood flow changes similar to those seen in umnedicated obsessive-compulsive symptoms. We have scanned one person on fluoxetine who received metergoline before the first scan and placebo before the second scan.